Preparing investments for casting



Mgrchl, 1949. c. A. MCFADDEN PREPARING INVESTMENT FOR `CASTING med sept. 26, 194e A INVENTOR. BYMMM ww n surface of the investment.-

uNiTsD s'rArss 'liwi'l'iau'r4 ori-ics marasma mvrsmrs Foncasrmc i Charles A'. McFadden, Upper Darby. Pa..

t9 Seial Corporation of America, Philad signor elphia,

This invention relates to investment molds.

n In casting by the investment method patterns or models formed of wax or like materials are embedded in an investment or investment mold formed of material which is inert with respect to the wax. 'Ille wax is then removed from the investment which is cured or baked to prepare it for casting. f

In order` to remove the wax the exterior of the investment usually is heated to convert the wax to gain access into the therein to a liquid Which flows by gravity from n the interior of the mold. The wax modelsv or patterns often are of intricate design and formed with traps from which melted wax cannot freely ow by gravity. In such cases the investment must be heated suiciently at the exterior thereof to bring the melted wax above its iiash point temperature, and they wax vapors thus formed pass from the interior of the investment through a sprue opening which extends'to a surface of the investment.

In removing wax from an investment in this manner, diillculty is often encountered to remove completely all of the wax from the interior of the investment. This is especially true when removing certain waxes from investments formed of material like cristobalite, for example.

Itis an object of the invention to provide an improvement for eectively removing all of the wax from an investment, particularly where difiiculty is ordinarily encountered because the wax tends to impregnate into the investment material.

The invention, together with the above and other objects and advantages thereof, will be better understood from the following description taken in conjunction with the accompanying drawing forming a part of this specification, and of which the single ligure illustrates one form of apparatus, partly broken away and in section, for practicing the invention.

In the drawing is more or less diagrammatically shown one form that an investment may take.

2 E heating space 20 therein for inserting and removing investments I into and from the heating space.

A .number of burners 2i are mounted in and form a part of the roof i1.' The burners 2i ,are incorporated in the roof I1 in any desired manner, the number and disposition of the burners being such that the desired heating oi the investment IU in the heating-space is effected.

The burners 2| preferably are'of a direct fired type capable of producing high heating temperatures in the heating space 20. Although not to be limited thereto.Y burners which have been found especially suitable are of the kind described and illustrated in Hess Patent No. 2,215,079, granted on September 17,1940. and, if desired, reference may be had thereto for a, detailed description of the burner structure.

'I'he heating'eiiects produced and developed in the heating space 20 include both radiant and convection heating components. The heat radiated from the burners2i, augmented by the convection heating derived from the heated products of combustion directed toward the investment I0 and downwardly in the heating space 20 provide heating effects for heating the investment IIJ rapidly to an elevated temperature.

A number of vertically -extending conduits 22 are incorporated in the side walls IB for withdrawing productsof combustion from the heating space 20. The lower ends of the conduits 22' terminate at the inner surfaces of .the side walls I6 adjacent the floor i8, and the upper ends thereof extend upwardly and terminate a short" distance from the roof l1 of the oven lli. At the upper ends of the conduits 22 are provided draft hoods 23 connected to a conduit 24 in which is provided a blower or exhaust fan 25.

By providing the draft hoods 28 the full effect of the exhaust fan will not be reflected back to the conduits 22 and cause too rapid withdrawal of the products of combustion from the heating B uch investment I Il is provided with a ask I,| l

in the form of a metal ring. Within the body of material forming the investment In a wax pattern or model I2 is embedded in a cavity having a sprueV opening I4 which extends to a The present'invention for completely removing all of the wax from the investment i0 is shown in connection with apparatus including a'n oven vor furnace i6 of a direct gas fired type having side walls I6, roof I1 and floor lll formed of a refractory material. A suitable door I8 is provided forthe oven in one of the side walls IB space 20. The-draft hoods 23 permit atmospheric .air to mix with the products of combustion to dilute and cool the exhausted gases, whereby provision need not be made for the conduit 24 and exhaust fan 25 to handle gases at an unduly high temperature.

A shell 28 isxed to the bottom of the floor I8 in any suitable manner. The floor i8 is provided with an opening 21 which is enlarged at its upper end to provide a cavity adapted to receive a sleeve memberv 28` upon which the investment I0 is adapted to rest. In the shell 26 is provided a tray 29 which is positioned beneath the opening 21 anales for collecting melted wax flowing. from the intenor or the investment le, as win be explained presently. The shell 26 is provided with a suitable closure member` 30 to gain. access therein.

When the investment I is being heated, hot wax vapors pass from the interior thereof into the shell 26. In order to dilute'such hot wax vapors with atmospheric air and also bring down the temperature of such vapors immediately upon passing into the shell 26, a side wall of the shell isprovided with one or more elongated slots or openings 3l to permit air from the surroundings to pass' into the interior of the shell. An exhaust iue 32 is connected at its lower end to the shell 26. and the upper` end thereof is connected to the conduit 24 so that the blower or exhaust fan2l will also be effective to withdraw the mixture of wax vapors and air from the shell 2l.

When the oven i0 is being operated the heating space is desirably maintained at an elevated temperature which may be in the neighborhood of 1200" to 1400 F., for example. The investment I0 rests snugly on the sleeve member 2B which in turn ilts tightly in the enlarged cavity of the opening 21. so that gas tight seals are ob-` tained between these parts. 'I'he investment Ill is heated to a desired high temperature by the heating ee'cts produced and developed in the heating space 20, whereby the wax model' I2 is melted and the wax flows by-gravity from the investment l0 through the opening 21 into the tray 29 in the shell 28. A

The products of combustion are withdrawn from the bottom part of the heating space 20 through the vertical conduits 22. and such spent e gases mix with air drawn into the draft hoods 23 by the exhaust fan 26. The mixture of air and the products of combustion may be dischargedv by the fan- 25 to the exterior of the enclosure in which the oven I5 is installed.

In manycases the wax models are of intricate design and formed with traps from which melted wax cannot freely ow by gravity, as .indicated at I3 in the drawing. Any melted wax which is trapped in the investment mold I0 is heated above its avsh point temperature. and the wax vapors thus formed pass from the investment Ill through -the opening 21 into the shell 28. The wax vapors passing into the shell 26 are'diiuted by relatively cool atmosphericair drawninto the shell through the opening or openings 3l by the action of the exhaust fan 25. The mixture ofwax vapors and air is withdrawn from the shell 26 through the -vertical ue 32 and mixes with the gases in conv bottom of the oor. I8. In this way wax vapors 4 by blocking the sprue opening I4 to increase the temperature to which the interior of the investment is heated. The sprue opening Il desirably is not blocked when the investment Il is initially heated but only after a maior portion of the wax flows in a liquid state from the interior of the investment.

In order to block the sprue opening Il in accordance with the present invention, a gate il is provided which is pivotally connected at to the bottom of the floor Il. When the investment I0 is initially heated, the gate remains in its solid line position and hangs vertically downward from its pivotal connection 34. After a maior portion and preferably substantially all of the melted wax. other than the melted wax in the traps Il, ilows by gravity from the investment Il into the tray 29, the gate 3l is moved to its horizontal position and locked in such horizontal position by a rotatable latch member 3l. as indicated in dotted lines in the drawing. -The gate 33 is moved from its open to its closed position by removing the closure member to gain access into the shell 26. n y J Although I do not wish to be limited thereto, it is my belief that certain waxes upon heating tend to impregnate into the investment material. With continued heating the wax impregnating the investment material then carbonizes. By blocking the sprue opening il after a substantial portion of the wax is removed from the investment I0 in a liquid state, heat losses from the interior of the investment are reduced and the temperature to which the interior of the investment is heated is increased, thereby facilitating the removalof the remaining wax from the investment The blocking of the sprue opening Il by the gate 33 is not complete in the sense that a sas tight sealis produced, but rather is of such a nature that gases can pass'through the blocked opening in the gap between the gate I3 and the expelled from the interior of the investment Il pass from the interior of the investment I0 in a path f flow out of physical contact with the heating space 20. When the heating of the investment lil is completed, the/ refractory invest.-

ment material is properly conditioned and a cavity is formed therein which is identical in conguratlon to the wax model I2 removed therefrom as a result of the heating just described.

In removing waxA from an investment mold in the manner just described, diillculty is often encountered to remove completely all of the wax canbe displaced by air in the shell 28 to promote oxidation of the carbonized wax material andinsure complete removal of the wax from the inf terior of the investment with a minimum amount of heatingand in the shortest possible length of time.

While the material forming the pattern is referred to as a wax in the foregoing description. it is` to be understood that this term in both the description and claim isl intended to cover not only waxes but also resins. plastics and like materials which aresuitable forv use in preparing investments of refractory material for casting.

Although I have shown and described a partici ular embodiment of my invention, it will be al parent to those skilled in the art that modica-4 tions and changes maybe made without departing from the spirit and scope of the invention as pointed outin the following claim.

What is claimed isz- Inthe art of removing an expendable pattern from'an investment that has a cavity in which the pattern is received and an opening extending fromv the surface of the investment to the cavity.

the improvement which consists in placing the investment in a heating space with said opening over an opening in the bottom of f said heating space. applying heat to said space to heat the in vestment to a temperature suillcient to liquefy the pattern so that it may flow byA gravity through the opening in the investment and the opening 5 in the heating space out of said heating space, and after the liquefied pattern has stopped now ing increasing the temperature of the heating space by blocking the heat losses through the opening in the bottom or `said heating space to 5 vaporize any of the pattern remaining in said cavity.

e A CHARLES A. McFADDEN.

REFERENCES crm The following references are of recoid in the 111e of this patent: t

o'rnmnmmmcns 1 I Refractory Molds for Precision Casting, The

Iron Age, Feb.l 8, 1945, page 57. 

